Observational and Modeling Studies of Radiative, Chemical, and Dynamical Interactions in the Earth''s Atmosphere

2 Pages·1998·0.09 MB·English

by  Salby, Murr

UNIVERSITY OF COLORADO
CENTER FOR ATMOSPHERIC THEORY AND ANALYSIS
Campus Box 391, Boulder, Colorado 80309-0391
Telephone [phone] Fax (303) 492-S524
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FINAL REPORT
Project Title: Observational and Modeling Studies of Radiative, Chemical, and Dy-
namical Interactions in the Earth's Atmosphere.
NASA Grant No: NAG-l-1355
PI: Murry Salby
Summary
A 3-dimensional model was developed to support mechanistic studies. The model solves
the global primitive equations in isentropic coordinates, which directly characterize di-
abatic processes forcing the Brewer-Dobson circulation of the middle atmosphere. It's
numerical formulation is based on Hough harmonics, which partition horizontal motion
into its rotational and divergent components. The formulation is spectral in all 3 coor-
dinates, the first global primitive equation model to be so. Scale-selective dissipation,
necessary for numerical stability, can then be imposed at 6th order - horizontally and
vertically. This leaves all but the shortest vertical scales undamped, on which advec-
tive transport can then be represented faithfully. These computational features, along
with others, enable 3D integrations to be performed practically on RISC computer
architecture, on which they can be iterated to support mechanistic studies.
The model conserves potential vorticity quite accurately under adiabatic conditions.
Forced by observed tropospheric structure, in which integrations are anchored, the
model generates adiabatic circulation that is consistent with satellite observations of
tracer behavior and diabatic cooling rates. The model includes a basic but fairly com-
plete treatment of gas-phase photochemistry that represents some 20 chemical species
and 50 governing reactions with diurnally-varying shortwave absorption. These species
combine with the diabatic circulation to yield a wintertime distribution of total ozone
that compares well with the observed by distribution from TOMS. The model thus
provides a reliable framework to study transport and underlying diabatic processes,
which can then be compared against chemical and dynamical structure observed and
in GCM integrations.
Integrations with the Langley GCM were performed to diagnose feedback between
simulated convection and the tropical circulation. These were studied in relation to
tropospheric properties controlling moisture convergence and environmental conditions
supporting deep convection, for comparison against mechanistic integrations of wave
CISK that successfully reproduce the Madden-Julian oscillation (MJO) of the tropical
circulation. These comparisons were aimed at identifying and ultimately improving
aspects of the convective simulation, with the objective of recovering a successful simu-
lation of the MJO in the Langley GCM, behavior that should be important to budgets
of upper-tropospheric water vapor and chemical species. They were not completed due
to premature termination of this grant.
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Publications
Salby, M., R. Garcia, and H. Hendon, 1994: Planetary-scale circulations in the presence
of climatological and wave-induced heating. J. Atmos. Sci., 51, 2344-2367.
Callaghan, P., A. Fusco, G. Francis, and M. Salby, 1998: A Hough spectral model for
3-dimensional studies of the middle atmosphere. J. Atmos. Sci. (Submitted).
Fusco, A. and M. Salby, 1998: Forcing of chemical distributions in the stratosphere by
planetary waves. J. Geophys. Res. (To be submitted).